FR2595178A1 - EARPHONE OF THE TYPE TO BE USED OUTSIDE - Google Patents

Abstract

THE INVENTION CONCERNS A HEADPHONE WHICH HAS A BOX 11 DIVIDED BY A CONTROL UNIT 12 INTO ANTERIOR CAVITES 18A AND POSTERIOR 18B, A SOUND-GENERATING OPENING SITUATED BEFORE THE ANTERIOR CAVITY, A CONDUCTING CONVERSION 27 AND A CAVITY POST HAVING A SUBSTANTIALLY LARGER LENGTH THAN ITS DIAMETER, AND A SPEAKER 31 FIXED TO THE CASE AND COMMUNICATING WITH THE POSTERIOR CAVITY THROUGH A LENGTH 32 LARGER THAN ITS DIAMETER, THE FREQUENCY OF RESONANCE DETERMINED BY THE SPEAKER AND THE CONDUCT THE FREQUENCY OF RESONANCE DETERMINED BY THE EQUIVALENT MASS OF THE VIBRATION SYSTEM, i.e. THE DIAPHRAGM 16 AND THE MOBILE COIL 17 OF THE CONTROL UNIT, AND THE ACOUSTIC ELASTICITY OF THE POSTERIOR CAVITY, THAT THE LOWEST RESONANCE FREQUENCY OF THE EARPHONE CAN BE LOWERED WHILE REMOVING THE PEAK WHICH WOULD NOT HAVE FAILED TO OCCUR IN THE EARPHONE FREQUENCY CHARACTERISTIC.

Description

The present invention relates generally to headphones and, more

  in particular, it aims to improve the acoustic characteristics of headphones of the type to be used outdoors, that is to say outdoors, in the low frequency range and in the high frequency range. Earphones of the external type according to the prior art have a housing housing a control unit and comprising a magnetic circuit and a vibration system

  consisting of a diaphragm and a voice coil. In sem-

  headphones of the outdoor type, the response decreases for frequencies below the resonant frequency

  of the vibration system and therefore the

  resonance quence has a low value to improve the characteristic at low frequencies. To reduce the frequency

  resonance, it is necessary to increase the elasticity acous-

  tick and / or the equivalent mass of the vibration system.

  To increase the acoustic elasticity of the vibration system,

  it is necessary to choose a material for the diaphragm

  dant a high acoustic elasticity and to decrease the thickness of the diaphragm. However, there are limits to the acoustic elasticity of the material that can be used for the diaphragm.

  and the extent to which the thickness of the diameter can be reduced

  phrase. In addition, increasing the equivalent mass of the vibration system leads to a deterioration in the sensitivity and acoustic characteristics of the earpiece in the range

high frequencies.

  To avoid the problems indicated above, the applicant has previously proposed, for example, as described in the Japanese utility model application No. 71055/1983, which was published without examination under No. 177287/1984 , that a headset or earphone to be placed in the ear is fitted with a hose leading from the housing to the rear of the control unit so that, when the earpiece has been placed in the ear , the pipe protrudes out of the conch, that is to say out of the outer ear. The pipe is formed so as to produce a

  equivalent mass added to the equivalent mass and the elastic-

  acoustic ticity of the vibration system, so that the resonant frequency is lowered in a way corresponding to the added equivalent mass of the pipe. Thus, the resonant frequency can be lowered independently of the acoustic elasticity and the equivalent mass of the vibration system, so that the characteristic of the earpiece can be improved in the range of

  low frequencies. However, this improvement in the character-

  In the low frequency range, there must be a significant acoustic resistance in parallel with the equivalent mass of the pipe, for example due to the presence of a material having a certain acoustic resistance in one or more openings formed in the housing. on the back of the control unit. However, in this case, a resonant circuit is formed by the mass of the vibration system and the acoustic elasticity of the housing at the rear of the control unit which is in parallel with the mentioned acoustic resistance. Due to the existence of such a resonance circuit, a peak appears in the frequency characteristic of the earpiece at frequencies from 3 to 5 kHz, that is to say that part of the range

  high frequencies is enhanced to the point that metal sounds

  liques become very striking and unpleasant to hear. In

  in other words, when we extend the range of low frequencies

  earpiece frequencies, an undesirable peak appears in the high frequency range and, conversely, when we try to remove this peak, we cannot extend the bass range

reproducible frequencies.

  It is therefore an object of the invention to provide a listener having an extended range for reproducible low frequencies and in which any resulting peak in the range

  high frequencies is effectively suppressed.

  More specifically, it is an object of the invention to provide an earphone with a housing which contains a control unit and is provided with a sound-generating opening in front of the control unit, and a pipe which leaves the case.

  behind the control unit to reduce the frequency of reso-

  lowest noise, particularly when the acoustic resistance of the housing behind the control unit increases and, moreover,

  o the extension obtained for the low frequency range repro-

  ductible is not accompanied by an increase or crest

  not desirable in the high frequency range.

  According to one aspect of the invention, a headset comprises a control unit, a housing containing the control unit and having a sound-generating opening in its front part, a pipe leaving the housing behind the control unit and communicating with the interior of the housing, this pipe having a length substantially greater than its diameter, and an enclosure fixed to the housing behind the control unit and communicating with the interior of the housing via a pipe whose length is greater than diameter. In the preceding assembly according to the invention, the resonance frequency

  of the resonant circuit constituted by the mass, or inertia, equivalent

  slow formed by the conduct and the acoustic elasticity formed by the enclosure is made close to the resonant frequency

  which is determined by the mass, or inertia, of the vibra-

  tion contained in the control unit and the acoustic elasticity of the housing behind the control unit, which allows

  remove the relatively high frequency peak which does not

  would not result from the resonance of the case back

  of the control unit and the mass of the vibration system.

  The following description, intended as an illustration

  tion of the invention, aims to give a better understanding of its characteristics and advantages; it is based on the annexed drawings, in which parts and corresponding elements are identified by the same reference numbers and o: FIG. 1 is a view in cross section showing an example of an earpiece according to the prior art; Figure 2 is an equivalent circuit diagram corresponding to the earphone of Figure 1; Figure 3 is a cross-sectional view showing another example of a prior art earphone; Figure 4 is a simplified perspective view showing the mounting of the earphone of Figure 3 in the ear of a user; Figure 5 is an equivalent circuit diagram corresponding to the earpiece of Figure 3; FIG. 6 is a graph showing characteristic curves of headphones according to the prior art; FIG. 7 is a cross-section view showing an earpiece according to a first embodiment of the invention; Figure 8 is an equivalent circuit diagram corresponding to the earpiece of Figure 7; Figures 9 and 10 are graphs showing frequency characteristics of headphones according to the invention, in comparison with headphones according to the prior art; and Figure 11 is a cross-sectional view showing

  a headset according to a second embodiment of the invention.

  To allow a better understanding of the problems which will be overcome by the invention, we will begin by referring to FIG. 1, which shows an earpiece 10 intended

  to be used outdoors according to the prior art. The neck-

  tor 10 comprises a housing 11 containing a control unit 12.

  The control unit 12 comprises a magnetic circuit formed by a magnetic plate 13, a carcass 14 and a magnet 15, and a vibration system formed by a diaphragm 16 and a voice coil 17 which is housed in an air gap appearing between the carcass 14 and the magnet 15. The control unit 12 extends across the casing 11 in the vicinity of a sound-generating opening located at the front of the housing, which has the effect of dividing the interior of the housing into a front cavity 18a and a rear cavity 18b. A hole 19 passes through the center of the control unit 12, and a material 20 having a certain acoustic resistance, for example urethane, or a material

  equivalent, is embedded in the hole 19. Several holes 21 tra-

  pour the plate 13 from the control unit 12 and are covered

  by a material 22 having a certain acoustic resistance.

  Several holes 23 are formed in the rear of the housing 11 and the rear cavity 18b communicates freely via these holes 23 with the surrounding atmosphere. A protective cover 24 extends across the sound-generating opening located at the front

2595 1 78

  of the housing 11 in order to prevent the diaphragm 16 from being damaged

  magé and an internal perforated metal sheet can be formed

  24a having relatively large holes, of a metallic sheet

  external perforated metal sheet 24b having relatively small holes and a film of fabric 24c lying between the

  metal sheets 24a and 24b in order to prevent the entry of pus-

  and other troublesome items. Conductive cables 25 leave from the control unit 12 and leave the housing 11 via a bushing, or insulating barrel, 26 located in

  a suitable hole formed in the side of the housing 11.

  The acoustic operating circuit of the

  tor 10 of the type for the exterior described above in relation to FIG. I can be expressed by the equivalent circuit of FIG. 2. More particularly, the vibration system of the control unit 12 is represented by a serial circuit an equivalent mass or inertia Md, an acoustic elasticity Cd and an acoustic resistance Rd. The force used to give

  forward and backward movement at the diaphragm 16 is shown

  sensed by a voltage source Vs, and Ra is the acoustic resistance offered to the passage of sounds through the acoustic resistance material 20 placed in the hole 19 and the acoustic resistance material 22 covering the holes 21 of the unit

  command 12. In the equivalent circuit of figure 2, the system

  posterior acoustic teme is represented by a parallel circuit

  formed of an acoustic elasticity Cb and an acous resistance

  tick Rb of the posterior cavity 18b. In addition, in FIG. 2, the acoustic elasticity, the equivalent mass and the acoustic resistance of the hole of the external ear in which the earpiece 10

  is inserted are represented by Ccup, Mcup and Rcup respectively.

  Since no resistant material covers or otherwise obstructs the passage of sound through the holes 23 of the rear of the housing 11, the acoustic resistance Rb of the posterior cavity 18b is so small that it can be ignored by comparison of the acoustic resistance Ra. Likewise,

  the acoustic elasticity Cb of the posterior cavity 18b can also

  be ignored due to the existence of holes 23 not covered

  green. Thus, the equivalent circuit of FIG. 2 can be

  considered as a series resonant circuit formed by the equilibrium mass

  valente Md, the acoustic elasticity Cd and the resistances

  ticks Rd and Ra of the vibration system. The resonant frequency f0 can therefore be expressed as follows: fo = 1 / (21.VM) (1) In the earphone of the type for the exterior according to the prior art which is represented in FIG. 1, the response decreases for frequencies below the resonance frequency fo0 of the vibration system. Thus, it is desirable that the resonance frequency fo0 can be made as small

  as possible to improve the characteristic of low frequencies.

  As follows from equation (1), the resonant frequency fo0 can be reduced by increasing the acoustic elasticity Cd, or else the equivalent mass Md of the vibration system. To increase

  the acoustic elasticity Cd of the vibration system, it is necessary

  choose a material with high elastic resistance for

  the diaphragm 16 and, or else, to decrease the thickness of the diaphragm.

  However, there are limits to the acoustic elasticity of the materials that can be used for the diaphragm, as well as to

  the extent to which the thickness of the diaphragm 16 can be reduced.

  In addition, the fact of increasing the equivalent mass Md of the vibration system produces a deterioration in the sensitivity and the acoustic characteristic of the earpiece 10 in the range of

high frequencies.

  We now refer to Figure 3. We can

  see that, to avoid the above problems, the request

  deresse previously proposed in the Japanese utility model published without examination under the number 177287/1984, which was cited above, to produce a 10 'earphone with a hose 27 starting from the housing 11' and communicating with the rear cavity 18'b of the housing. As shown in Figure 4, we see that the earpiece 10 'is intended to be inserted into the outer ear E of the user so that an end portion of the pipe 27 protrudes outside the shell. The parts of the earpiece 10 'which are identical to parts of the earpiece 10 previously described in relation to FIG. 1 are identified by the same reference numbers and

  we will not repeat a detailed description of these.

  It will be noted that, in the earpiece 10 ′, the holes or openings 21 formed in the plate 13 are uncovered, that is to say that the acoustic resistance material 22 has been omitted

  of FIG. 1, so that the acoustic resistance Ra is sensitive

  badly zero. However, an acoustic resistance material 28 was applied to each of the holes or openings 23 located at the substantially frustoconical rear part of the housing 11 ′, so that the acoustic resistance Rb is thus fixed at a value

  sufficient, for a reason which will be indicated in detail below.

  An elastic ring 29 of rubber, or of a material

  riau analog, is placed around the sound-generating opening located at the front of the housing 11 'to prevent sound leakage between the plate 13 and the housing 11' and between the plate 13 and the protective cover 24. Des openings 30 are formed in the end part of the pipe 27 remote from the housing 11 '. The pipe 27 has a length substantially greater than its diameter, for example a length of 12 mm and a diameter of 2.2 mm, in which case the pipe 27 can be represented by an equivalent mass Mduct

  adding to the series circuit the equivalent mass Mt, the elastic-

  acoustic tness Cd and acoustic resistances Rd and Ra of the vibration system. Thus, the resonant frequency fO decreases

  by an amount corresponding to the equivalent mass Mduct added.

  This reduction in the independent resonance frequency fo is obtained.

  especially the acoustic elasticity Cd and the equivalent mass Md of the vibration system in order to improve the characteristic of

  the earpiece in the low frequency range.

  It should be noted that the lowest resonance frequency fo of the earpiece 10 ′ can be reduced by producing a pipe 27 as described above in the only case where the acoustic resistance Rb which is in parallel with the ground equivalent Mduct of pipe 27 is substantially greater than zero. In other words, to achieve the effect of the equivalent mass Mduct in a sensitive way, it is necessary to increase the acoustic resistance Rb by placing

  the acoustic resistance material 28 above the openings 23.

  For example, as shown in FIG. 6, when the acoustic resistance Rb is increased by appropriately changing the material, the thickness, or a similar parameter, of the acoustic resistance material 28 associated with the openings 23, the characteristic curve of the earpiece varies, as indicated by curves A, B and C. However, when the acoustic resistance Rb is increased, a resonant circuit is formed by the acoustic elasticity Cb, which is in parallel with the acoustic resistance Rb, and the mass Md of the vibration system. Due to such a resonant circuit, it

  a peak appears in the frequency characteristic of the listening

  tor for frequencies from 3 to 5 kHz, that is to say that a part of the high frequency range is reinforced, as shown in FIG. 6, so that the metallic sounds become very

  striking and unpleasant to hear. So, in the case of listening

  According to the prior art as shown in FIG. 3, when the range of the low frequencies of the earpiece is extended downwards, an undesirable peak appears in the range of high frequencies, while, when the we remove this peak, we can no longer extend the range of reproducible low frequencies.

  We now refer to Figure 7, which represents

  feels a 10A earpiece according to an embodiment of the invention,

  which is generally analogous to the earpiece 10 'described in rela-

  tion with figure 3, the corresponding parts being identi-

  relied on by the same reference numbers. As before, the

  housing 11 ′ has an approximately truncated rear part

  conical and, in the case of the 10A earpiece, an approx.

  matively cylindrical 31 is suitably fixed to the center of this frustoconical rear part of the housing 11 '. The enclosure 31 and the rear cavity 18'b of the housing 11 communicate with each other by means of a pipe 32 which enters centrally in the enclosure 31. An opening 33 is formed in the central part of the rear wall of the enclosure 31, and an acoustic resistance material 34, for example urethane or a material

  equivalent, extends in this opening 33.

  In a practical example of the earpiece 10A according to the invention, the magnet 15 of the control unit 12 'is formed of cobalt-samarium, and the diaphragm 16 is made of a film of

  polyethylene having a thickness of 6 µm. Pipe 27 has a diameter

  meter of 2.2 mm and a length of 12 mm, while the pipe 32 also has a length greater than its diameter, for example a length of 1.5 mm and a diameter of 1 mm. Finally, the enclosure 31 has an internal volume of 70 mm3. We now refer to FIG. 8, where we can see the acoustic equivalent circuit of the earpiece 10A according to the invention, which differs from that presented in the figure. 5 for the earpiece 10 ′ of the prior art due to the addition

  to the latter of an equivalent mass Mtt, of an elasticity acous-

  tick Ctt and an acoustic resistance Rtt corresponding to the

  line 32, enclosure 31 and opening 33 respectively.

  In FIG. 8, as in FIG. 5, the equivalent mass Mduct

  of the hose 27 is added to the series circuit consisting of the earth

  valente Md, the acoustic elasticity Cd and the resistance

  tick Rd of the vibration system, so that the lowest resonant frequency fo0 decreases in relation to the added amount of the equivalent mass Mduct Such a lowering of the lowest resonant frequency fo0 by the equivalent mass

  added Mduct is made possible by the notable value of the resistance

  acoustic resistance Rb which results from the material of resistance

  tick 28 covering the openings 23. However, due to the equivalent mass Mtt formed by the pipe 32, the elasticity

  acoustic Ctt formed by the enclosure 31 and the resistance

  tick Rtt formed by the opening 33 covered with the resistance material

  acoustic tance 34, the peak which would otherwise have occurred in the frequency range 3 to 5 kHz by the resonance existing between the equivalent mass M of the vibration system and

  the acoustic elasticity Cb of the posterior cavity 18'b is greater

  award-winning. More specifically, a resonant circuit is formed by the equivalent mass Mtt of the pipe 32 and the acoustic elasticity Ctt of the enclosure 31. Thus, the impedance across the circuit consisting of the equivalent mass Mtt, of the acoustic elasticity Ctt and the acoustic resistance Rtt decreases at the resonance frequency of this resonant circuit. This is why, by choosing the resonance frequency of the resonant circuit formed by the equivalent mass Mtt and the acoustic elasticity Ctt at a value close to the resonance frequency of the circuit constituted by the equivalent mass Md of the vibration system and the acoustic elasticity Cb of the posterior cavity 18'b, it is possible to conveniently remove the crest which would not have otherwise failed to be produced by the equivalent mass Md and the elasticity

  acoustics Cb in the frequency range 3 to 5 kHz.

  As can be seen in FIG. 9, where the curve D1 in solid line represents the frequency characteristic of the earpiece 10A according to an embodiment of the invention and the curve DO in broken line represents the frequency characteristic of l 'earpiece 10' according to the prior art as shown in Figure 3, the peak appearing in the frequency range from 3 to 5 kHz for the earpiece according to the prior art is substantially eliminated in the case of the earpiece 10A according to l 'invention. The curves DO and D1 in FIG. 9 respectively represent the frequency characteristics of the earphones 10 '

  and 10A, insofar as these 10 'and 10A headphones have

  roughly the same values for the acoustic resistance Rb.

  However, if this is desirable, the acoustic resistance Rb of the earpiece 10A according to the invention can be significantly increased compared to the acoustic resistance Rb of the earpiece according to the prior art, so as to further reduce

  the lowest resonant frequency fo of the earphone 10A is

  constituting an embodiment of the invention without increasing the peak of the frequency range from 3 to 5 kHz beyond that appearing in the frequency characteristic of the earpiece 10 'according to the prior art. Thus, for example, in FIG. 10, the curve D2 indicates the frequency characteristic of a headphone according to the invention where the acoustic resistance Rb has been increased beyond the corresponding value of the acoustic resistance Rb of the headphone 10 'according to the prior art shown in Figure 3 and having the frequency characteristic of the DO curve. It clearly results from a comparison between the curves DO and D2 that, if the peaks of the frequency range from 3 to 5 kHz can be almost equal for the headphones according to the invention and according to the prior art, it is possible to

  lower the lowest resonant frequency fo for listening

  tor according to the invention compared to the headphone according to the technique

  earlier, for example at 100 Hz compared to 150 Hz.

  While Figure 7 shows the invention material-

  read in the form of an earpiece in which the enclosure 31 has an opening, or hole, 33 in its rear face, which is coated with the acoustic resistance material 34, it should be understood that the invention can also be embodied in a earpiece 10B as shown in Figure 11 and o the enclosure 31 'defines a closed chamber which communicates only with the cavity

  rear 18'b of the housing 11 'via the connector

  pick 32. Apart from what has just been stated, that is to say apart from the omission of the hole 33 and of the acoustic resistance material 34 in the enclosure 31 ′, the earphone lOB is substantially identical to the 10A earpiece and its various parts are identified by the

same reference numbers.

  In the case of the earphone lOB represented in FIG. 11, when the volume of the enclosure 31 'is 70 mm3 and the value of the acoustic resistance Rb is increased in the same way as for the earphone represented by the curve D2 of figure 10, the frequency characteristic of the earpiece is represented by the curve D3. In other words, the fact

  to remove the hole, or opening, 33 in the enclosure 31 of the drain

  10A has the effect of shifting the crest of the range of

  frequencies from 3 to 5 kHz at a frequency close to 2 kHz. Such displacement of the peak of the frequency characteristic tends to make the metallic sounds less remarkable. If the volume of the speaker 31 'of the lOB earpiece is increased to 300 mm, the frequency characteristic becomes that indicated by the

  curve D4 in Figure 10. In this case, the peak is less pro-

  uttered and the frequency characteristic is somewhat flattened.

  However, to obtain an enclosure with a volume of 300 mm3,

  the enclosure must be increased to an undesirable degree.

  While the invention has been described above in its application to headphones of the type to be put in the ear, and the headphones are placed near the entrance to the orifice of the outer ear, it is necessary note that the invention can be applied analogously to headphones intended for a closed environment, that is to say headphones intended to be

  used indoors. In addition, we will obtain particularly

  the desirable effects of the invention when applied

  quera associated stereo headphones respectively

  to the right ear and the left ear of the listener.

  In summary, it will be noted that the resonant circuit cons-

  with the equivalent mass Mtt formed by line 32 and

  the acoustic elasticity Ctt formed by the enclosure 31 or 31 'pos-

  sedes a resonant frequency which is fixed at a value close to the resonant frequency of the acoustic elasticity Cb of the

  posterior cavity 18'b and mass Md of the vibration system.

  Because of what has just been stated, the crest of the character-

  frequency ristic which is due to the resonance between the posterior cavity and the mass of the vibration system is suppressed in

  some measure. Thus, it is possible to improve the character-

  teristic for high frequencies and we can increase the acoustic resistance Rb to decrease the resonant frequency

the lowest fO.

  Of course, those skilled in the art will be able to ima-

  giner, from the earpiece whose description has just been

  given for illustrative purposes only and in no way limitative, various variants and modifications not beyond the scope of

the invention.

Claims (11)

R E V E N D I C A T I 0 N S   1. Headphone, characterized in that it comprises: a control unit (12 '); a housing (11 ') containing said control unit and having a sound-generating opening at the front of said control unit; a pipe (27) projecting from said housing in   rear of said control unit and communicating with the interior   laughing of said housing, the pipe having a diameter and a length which is substantially greater than said diameter; an enclosure (31, 31 ') fixed to said housing behind said control unit; and   means defining a pipe (32) which commu-   nique respectively, by its ends, with said housing and said enclosure and which has a diameter and a length more   larger than said pipe diameter.   2. Headphone according to claim 1, characterized in that the enclosure (31) has an opening (33) communicating with the atmosphere, a material of acoustic resistance (34)   extending across said opening of the enclosure.   3. Headphone according to claim 1, characterized in that said enclosure (31 ') defines a closed chamber which communicates only with said housing via said pipe. 4. Headphone according to claim 1, characterized in   that the control unit includes a means (13, 14, 15) defined   forming a magnetic circuit, as well as a diaphragm (16) and a moving coil (17) which form a vibration system, and in that the resonance frequency of a resonant circuit consisting of an equivalent mass (Mtt) formed by said pipe (32) and an acoustic elasticity (Ctt) formed by said enclosure (31, 31 ') is made closer to the resonance frequency (fo0) which is determined by the mass, or inertia, (Md) of said vibration system and the acoustic elasticity (Cb) of said housing at the rear of the unit control.   5. Headphone according to claim 4, characterized in that the housing has an opening (23) at the rear of the control unit, and an acoustic resistance material (28) extends   across said opening of the housing in order to lower the   lowest resonance quence determined by the mass of the vibration system and the acoustic elasticity of the housing behind the control unit, while the resonant circuit formed by said pipe and said enclosure eliminates a relatively high frequency peak which would not fail otherwise   not produce in the frequency characteristic of the earphone.   6. Headphone according to claim 5, characterized in that the enclosure (31) has an opening (33) communicating with the atmosphere, an acoustic resistance material (34)   extending across the opening of the enclosure.   7. Headphone according to claim 5, characterized in   what the enclosure (31 ') defines a closed chamber which does not   only with the box through the pipe.   8. Headphone according to claim 1, characterized in that the control unit (12 ') comprises a magnetic circuit consisting of a plate (13) extending across the housing and dividing the latter into a rear cavity (18 'b) and a front cavity (18'a) communicating with said sound-generating opening, a magnet (15) and a carcass (14), and a vibration system consisting of a diaphragm (16) s extending across said housing in said anterior cavity and a voice coil (17) connected to said diaphragm, and in that the frequency of   resonance of a resonant circuit made up of the equivalent mass   slow (Mtt) formed by said pipe (32) and the elasticity acous-   tick (Ctt) formed by said enclosure (31, 31 ') is made close to the resonance frequency (f0o) which is determined by the mass (Md) of said vibration system and the acoustic elasticity (Cb)   of the posterior cavity, and the plate (13) of the   Mande has holes which pass freely through it to make   communicate said anterior and posterior cavities.   9. Headphone according to claim 8, characterized in that the housing has an opening (23) in its rear cavity (18'b), a material of acoustic resistance (28)   extending across this opening to lower the frequency   lowest resonance quence (fo0) determined by mass (Mt)   of the vibration system and the acoustic elasticity (Cb) of the   posterior vity, while the resonant circuit constituted by the pipe (32) and the enclosure (31, 31 ') suppresses a peak of relatively high frequency which would not fail if not to be   occur in the frequency characteristic of the earphone.   10. Headphone according to claim 9, characterized in that the enclosure (31) has an opening (33) communicating   with the atmosphere, in which a material of resistance pushes tick (34) is disposed.   11. Headphone according to claim 9, characterized in   what the enclosure (31 ') defines a closed chamber which does not   only with said rear cavity of the housing through the conduct medium.